The problem is the oil is locked inside the rock and until now, nobody's found a cheap way to get it out.

NPR: Industry Seeks to Extract Oil from Rocky Mountain Shale

The grey stands in contrast to the weathered red outer-coating of the Sheepbed unit, and the darker colour hints at a different oxidation state for iron (Fe) minerals that might be inside the rock.

BBC: Nasa's Curiosity Mars rover to ingest drill sample soon

Scientists have found creatures thriving in places that would poison or cook most life on earth--deep inside rock, under the ocean or in hot springs, places that are extremely salty, or acidic, or bathed in radiation or heavy metals.

FORBES

If disaster strikes and a LFTR springs a leak, the spill cools to an inert lump of rock, chemically locking all the nuclear material inside.

FORBES: UK Parliament Group to Study Thorium Reactors

On Earth, sea-floor spreading is fuelled by molten rock upwelling from deep inside the Earth.

BBC: Enceladus has 'spreading surface'

Imaging techniques are so good that geologists can approximate standing inside a rock formation to look for the spots most likely to hold oil.

FORBES: Technology

The industry has boomed in recent years, thanks to a stunning expansion of drilling in previously untapped areas because of the use of hydraulic fracturing, or fracking, which injects sand, water and chemicals to break apart rock and free the gas inside.

NPR: EPA Methane Report Further Divides Fracking Camps

Drilling a few centimetres inside a rock provides a fresh sample that is free from the alteration that can occur at the surface as a result of weathering or radiation damage.

BBC: Curiosity Mars rover hammers into rock

The rover hit pay dirt early, landing inside a shallow crater ringed in layered rock outcroppings.

CNN: Mars rovers working overtime